*52 
Digby . — ( 9/2 the Archesporial and 
sionally found tripolar spindles, but he considers them to be abnormal 
stages in spindle development. 
The chromosomes retreat before the encroaching fibres towards the 
centre of the nucleus, and fission is sometimes evident in the univalent 
segments (PL XI, Fig. 80). The nuclear limiting membrane disappears, 
the fibres invade the nucleus (Fig. 81), and the chromosomes collect towards 
the centre of the nucleus. 
Heterotype Metaphase, Anaphase, and Telophase. 
The chromosomes then arrange themselves on the spindle (Fig. 82), 
which has now become bipolar. The number of chromosomes as seen in 
polar view of an equatorial plate of O. palustris, var. aurea , is apparently 
20 (Fig. 83) ; the reduced number both in O. regalis ( 17 , 11 , 13 ) and in 
O. cinnamomea ( 19 , 13 ) is 22. 
Disjunction of the entire univalent chromosomes of each bivalent pair 
takes place on the equatorial plate, and it is immediately succeeded by 
a cleavage in the substance of each entire chromosome, widely separating it 
into diverging halves. This is the first sign of dissociation of the threads of 
spireme which associated in pairs during the presynaptic and synaptic 
stages, and is therefore the opening out of the fission so clearly seen in the 
entire univalent post-synaptic spireme (filament). 
Fission in the univalent chromosomes as they proceed to the hetero- 
type spindle poles is so extensive as to split each chromosome into a V, the 
apex of the V pointing to the pole (Fig. 84) (see Text-fig., No. 25). This pre- 
cocious cleavage may be attributable to the fact that entire univalent chromo- 
somes are passing to the poles, a phenomenon peculiar to the heterotype 
mitosis. These daughter chromosomes will finally separate on the homotype 
spindle. The cleavage continues to be very marked when the chromosomes 
are looked at in polar view of early anaphase (Fig. 85), and it causes each 
chromosome to be double, thus making it difficult to obtain an accurate count. 
The chromosomes draw together and a further and new fission appears 
in the substance of each daughter chromosome, giving it a fenestrated or 
vacuolated appearance (Fig. 86) (see Text-fig., No. 26). This new fission in 
the daughter chromosomes of the heterotype telophase is homologous with the 
fission in the daughter chromosomes, of a somatic telophase. It is prophetic 
of the post-ho 7 notypic division, and reappears in the early anaphase and telo- 
phases of the homotype mitosis, thereby splitting the daughter chromosomes 
(Fig. 98) into longitudinal halves (threads) (see Text-fig., Nos. 31, 33, 34, 
and 35). 
This double fission becomes intelligible when it is remembered that 
entire univalent premeiotic chromosomes are distributed to the poles of the 
heterotype spindle, instead of half or daughter univalent chromosomes, as 
in somatic divisions. Consequently, not only does the whole univalent 
